Many surgical, diagnostic, therapeutic and prophylactic medical procedures require the placement of objects such as sensors, treatment units, tubes, catheters, implants and other devices within the body. These procedures cover a large spectrum including, for example:                insertion of electrodes for therapeutic or diagnostic purposes,        placement of tubes to facilitate the infusion of drugs, nutritional and other fluids into a patient's circulatory system or digestive system,        insertion of probes or surgical devices to facilitate cardiac or other types of surgery, and        biopsies or other diagnostic procedures.        
In many instances, insertion of a device is for a limited time, such as during surgery or catheterization. In other cases, devices such as feeding tubes or orthopedic implants are inserted for long-term use. The need exists for providing real-time information for accurately determining the location and orientation of objects within the patient's body, preferably without using X-ray imaging.
U.S. Pat. Nos. 5,391,199 and 5,443,489 to Ben-Haim, whose disclosures are incorporated herein by reference, describe systems wherein the coordinates of an intrabody probe are determined using one or more field sensors, such as a Hall effect device, coils, or other antennae carried on the probe. Such systems are used for generating three-dimensional location information regarding a medical probe or catheter. Preferably, a sensor coil is placed in the catheter and generates signals in response to externally-applied magnetic fields. The magnetic fields are generated by three radiator coils, fixed to an external reference frame in known, mutually spaced locations. The amplitudes of the signals generated in response to each of the radiator coil fields are detected and used to compute the location of the sensor coil. Each radiator coil is preferably driven by driver circuitry to generate a field at a known frequency, distinct from that of other radiator coils, so that the signals generated by the sensor coil may be separated by frequency into components corresponding to the different radiator coils.
U.S. Pat. No. 6,198,963 to Ben-Haim et al., whose disclosure is incorporated herein by reference, describes simplified apparatus for confirmation of intrabody tube location that can be operated by nonprofessionals. The initial location of the object is determined as a reference point, and subsequent measurements are made to determine whether the object has remained in its initial position. Measurements are based upon one or more signals transmitted to and/or from a sensor fixed to the body of the object whose location is being determined. The signal could be ultrasound waves, ultraviolet waves, radio frequency (RF) waves, or static or rotating electromagnetic fields.
PCT Patent Publication WO 96/05768 to Ben-Haim et al., whose disclosure is incorporated herein by reference, describes a system that generates six-dimensional position and orientation information regarding the tip of a catheter. This system uses a plurality of sensor coils adjacent to a locatable site in the catheter, for example near its distal end, and a plurality of radiator coils fixed in an external reference frame. These coils generate signals in response to magnetic fields generated by the radiator coils, which signals allow for the computation of six location and orientation coordinates.
U.S. Pat. No. 6,239,724 to Doron et al., whose disclosure is incorporated herein by reference, describes a telemetry system for providing spatial positioning information from within a patient's body. The system includes an implantable telemetry unit having (a) a first transducer, for converting a power signal received from outside the body into electrical power for powering the telemetry unit; (b) a second transducer, for receiving a positioning field signal that is received from outside the body; and (c) a third transducer, for transmitting a locating signal to a site outside the body, in response to the positioning field signal.
U.S. Pat. No. 6,172,499 to Ashe, whose disclosure is incorporated herein by reference, describes a device for measuring the location and orientation in the six degrees of freedom of a receiving antenna with respect to a transmitting antenna utilizing multiple-frequency AC magnetic signals. The transmitting component consists of two or more transmitting antennae of known location and orientation relative to one another. The transmitting antennae are driven simultaneously by AC excitation, with each antenna occupying one or more unique positions in the frequency spectrum. The receiving antennae measure the transmitted AC magnetic field plus distortions caused by conductive metals. A computer then extracts the distortion component and removes it from the received signals, providing the correct position and orientation output.
U.S. Pat. No. 4,173,228 to Van Steenwyck et al., whose disclosure is incorporated herein by reference, describes a catheter locating device based upon inducing a signal in a coil attached to the catheter and monitoring the amplitude and phase of the induced signal.
U.S. Pat. No. 5,099,845 to Besz et al., and U.S. Pat. No. 5,325,873 to Hirschi et al., whose disclosures are incorporated herein by reference, describe apparatus and methods in which a radiating element is fixed to a medical tube, e.g., a catheter, and the position of the tube is determined responsive to energy radiated from the element.
U.S. Pat. No. 5,425,382 to Golden, et al., whose disclosure is incorporated herein by reference, describes apparatus and methods for locating a medical tube in the body of a patient by sensing the static magnetic field strength gradient generated by a magnet fixed to the medical tube.
U.S. Pat. No. 4,905,698 to Strohl et al. and U.S. Pat. No. 5,425,367 to Shapiro, et al., whose disclosures are incorporated herein by reference, describe apparatus and methods wherein an applied magnetic field induces currents within a coil at the tip of a catheter. Based on these currents, the relative location of the catheter is determined.
U.S. Pat. No. 5,558,091 to Acker et al., whose disclosure is incorporated herein by reference, describes a magnetic position and orientation determining system which uses uniform fields from Helmholtz coils positioned on opposite sides of a sensing volume and gradient fields generated by the same coils. By monitoring field components detected at a probe during application of these fields, the position and orientation of the probe is deduced. A representation of the probe is superposed on a separately-acquired image of the subject to show the position and orientation of the probe with respect to the subject.
U.S. Pat. No. 5,913,820 to Bladen et al., whose disclosure is incorporated herein by reference, describes apparatus for locating the position of a sensor, preferably in three dimensions, by generating magnetic fields which are detected at the sensor. The magnetic fields are generated from a plurality of locations and enable both the orientation and location of a single coil sensor to be determined.
Commercial electrophysiological and physical mapping systems based on detecting the position of a probe inside the body are presently available. Among them, CARTO™, developed and marketed by Biosense Webster Inc., Diamond Bar, Calif., is a system for automatic association and mapping of local electrical activity with catheter location.
An article entitled, “Microtool Opens 3D Window into the Human Body,” by Cleopatra Alfenito, Medical Imaging 12(11) (November, 1997), which is incorporated herein by reference, describes the “miniBIRD” device, made by Ascension Technology (Burlington, Vt.). This device “ . . . measures internal organs and their motion by reconstructing the position and orientation of 2D slices to fill a 3D volume . . . Sensors—as small as 5 mm—can be attached to probes, instruments, or even a fetal head inside the human body. These mini-trackers measure the spatial location of ultrasound probes or other instruments with six degrees of freedom (position and orientation as given by x,y,z, yaw, pitch and roll) in real time. The miniBIRD works by measuring magnetic fields and converting signals to real-time 3D measurements. At the start of each measurement cycle (of which there are up to 144 per second), the system's triaxial transmitter is driven by a pulsed DC signal. The sensor then measures the transmitted magnetic field pulse. The electronics unit controls the transmitting and receiving elements and converts the received signals into real-time position and orientation measurements, providing for the collection of accurate data. This data can then be used for 3D reconstruction of internal images of the heart, blood vessels, stomach, pelvis and other areas as provided by ultrasound or an endoscope.”